1. Field of the Invention
The present invention relates to process and an apparatus for a semiconductor growth and more particularly, to a CVD process for producing a semiconductor epitaxial layer, and a CVD apparatus therefor.
2. Description of the Related Art
To form a thin epitaxial layer of a semiconductor material such as a silicon (Si), silicon germanium (SiGe) silicon carbide (SiC), etc., a CVD (Chemical Vapor Deposition) process, a MBE (Molecular Beam Epitaxial) process, a photo epitaxial growth process etc., are used.
Since an epitaxial growth by the CVD process is carried out at a comparatively high temperature of to 1200.degree. C., for a long time, a greater diffusion than required is generated, and thus a satisfactorily shallow pn junction cannot be formed.
On the other hand, as an epitaxial growth process at a comparatively low temperature, e.g., 600 to 700.degree. C., an MBE process and a photo epitaxial growth process are well known.
The MBE process, however, has problems in that the process is not suitable for mass production because of the necessity for a high vacuum condition, the poor crystallizability of a formed epitaxial layer, an epitaxial growth cannot be realized at a side wall of a semiconductor substrate, a selective growth cannot be carried out, and impurities cannot be doped into a semiconductor substrate to a high concentration, e.g., more than 10.sup.18 /cm.sup.3.
Further, the photo epitaxial growth process has problems in that a mass productivity thereby defective in that the window for introducing the UV light becomes fogged, and an epitaxial growth cannot be realized at a side wall of a semiconductor substrate.
In the above-mentioned problems, when impurities are not diffused at a required level when forming different layers, the interface therebetween is not clearly defined, i.e., a sharp distinction in layer boundaries cannot be observed. Thus, due to the non-distinctiveness of the boundaries therebetween, the amplification factor of the device becomes poor and the cut-off frequency f.sub.T is lowered with the result that the circuit transmitting speed is lowered.